Common rail diesel fuel injection systems have enable diesel engines to operate with increased fuel efficiency, reduced noise, and reduced emissions. The common rail diesel injection system first pressurizes fuel under high pressure in a central accumulator rail and then delivers it to the individual electronically-controlled injection valves/injectors. The pressurized fuel is used for combustion and injector operation. In addition, fuel is also used to cool and lubricate the pumping apparatus. This provides high injection pressures, in some cases over 25,000 psi, across a wide range of operating conditions. The common rail injection system may allow up to 5 injections per engine cycle. However, one issue associated with the common rail fuel injection system is the amount of heat added to the fuel not used for combustion. The unburned/return fuel temperature can reach up to 140° C., for example. The elevated fuel temperature may cause deterioration of the fuel pump efficiency and durability, degradation of plastics and elastomers, and require hydrocarbon traps in the fuel system. Various cooling systems may be used to cool the returning fuel to address the above issues.
One such fuel cooling system for diesel injection system is described in U.S. Pat. No. 6,868,838. This system includes two cooling devices for cooling un-injected fuel returning from the common rail fuel injection system to the fuel tank. The first cooling device (a water/fuel exchanger) is positioned downstream of the engine; and the second cooling device (an air/fuel exchanger) is positioned downstream of the first cooling device. A control device controls the position of the various valves in the cooling system to determine the returning fuel flow route. The returning fuel can either pass through or bypass any one of the cooling devices depending on the valve positions. This results in various degrees of fuel cooling. The control device controls the valve based on the ambient temperature and the engine speed. For example, at a low ambient temperature, on the order of −20° C., and a medium engine speed, since no cooling of the fuel is required, the control unit directs the valves to be in such positions that returning fuel bypasses both cooling devices. Likewise, at a very high exterior temperature, on the order of 80° C., and high engine speed, since maximum cooling of the returning fuel is needed, the control unit directs the valves to be in such positions that the returning fuel passes through both cooling devices. Further, at a hot ambient temperature, on the order of 40° C., and a low engine speed, since moderate cooling of the returning fuel is needed, the control unit directs the valves to be in such positions that the returning fuel bypasses the first cooling device but passes through the second cooling device.
However, the inventors herein have recognized several issues with the above approach. For example, the use of two cooling devices in combination with multiple control valves may increase a likelihood of mechanical or electrical degradation of the system, and thus during some conditions inadequate cooling may result. Further, it may be difficult to control the returning fuel temperature with sufficient accuracy through coordination of the different valve positions.
The inventors herein have recognized that such issues may be at least partially addressed by providing a fuel cooling system for a diesel engine system having a set of internal combustion cylinders, a fuel storage tank, and a common rail fuel injection system which comprises (1) a fuel distribution circuit for carrying fuel from the fuel storage tank to the common rail fuel injection system to be injected into the engine cylinders; (2) a fuel recycling circuit for carrying un-injected fuel returning from the common rail fuel injection system back to the fuel storage tank; (3) a temperature sensor for sensing fuel temperature; (4) a fuel to coolant heat exchange system for cooling the fuel wherein the fuel to coolant heat exchange system comprises a coolant reservoir, an electric coolant pump, and a heat exchanger; (5) a mechanism for controlling the electric coolant pump operation; (6) an air to coolant heat exchange system coupled to the fuel to coolant heat exchange system for cooling the coolant in the fuel to coolant heat exchange system wherein the air to coolant heat exchanger system is exposed to vehicle ram air and includes a heat exchanger and a cooling fan; (7) and a mechanism for controlling the cooling fan.
In some embodiments, the control mechanisms for controlling the coolant pump and the cooling fan may be provided by a control system, such as an engine control unit, where control of the pump and cooling fan may vary with operating conditions of the vehicle.
In some embodiments, it is possible the fuel cooing system may contain a routine for performing temperature sensor diagnostics. In some other embodiments, the fuel cooling system may further be able to switch to a temperature sensor degradation strategy for controlling the coolant pump and/or for controlling the cooling fan in case the temperature sensor is not working properly.
By providing both an air to coolant heat exchange system in addition to a fuel to coolant heat exchange system, the fuel cooling system may achieve additional cooling that may not be possible through a fuel to coolant heat exchange system alone. Further, by coordinating control of the cooling fan and cooling pump, appropriate cooling can be tailored to the vehicle operating conditions to achieve improved fuel cooling and performance. For example, the fuel cooling system may provide an supplemental cooling when the vehicle ram air is not sufficient, for example when the vehicle is operating at an lower engine speed or when the vehicle ram air is impeded by for example a physical block.
Finally, by providing a fuel temperature sensor degradation strategy, the fuel cooling system may reduce fuel system shut-downs and provide necessary cooling even when the fuel temperature sensor degrades.